The present invention relates to a motor-assisted bicycle that transmits driving force from a motor or the like so as to run with the driving force as a driving source.
Conventionally a motor-assisted bicycle of this type, as described in Japanese Unexamined Patent Publication No. 58568/1997 (B62M23/02), is designed to have a pulley provided on an output shaft of a motor, rotate the next pulley through a belt engaged on the pulley, and couple the pulley to a gear formed on an inner periphery of a rotational casing so as to transmit driving force. By provision of a one-way clutch in the pulley, the rotation by the motor driving force can be cut off, when the rotation speed of a wheel becomes faster than the rotation by the motor driving force, so that the motor driving force does not become the load of rotation of the wheel with making the rotation of the wheel preferential.
A tension pulley is provided in the middle portion of a belt to adjust the tension of the belt, so that the loss in transmission of the driving force is reduced by pressing the belt with the tension pulley.
However, this configuration has problems in that the entire casing cannot be made smaller, even if an attempt is made to make it lighter in weight and more compact in shape due to the increased number of the pulleys, and that the number of components increases because the one-way clutch has to be provided as a separate item in addition to the pulley, which takes more time in the assembly operation and increases the cost.
Since the tension pulley has to be used, the casing becomes larger. Further, the number of components is increased, whereby the assembly time is increased and the cost becomes higher.
The present invention was made in view of the above drawbacks, and an object of the invention is to provide a motor-assisted bicycle which is lighter in weight, more compact in shape, has a reduced number of components, and is easier to assemble.